1. Field of the Invention
The invention relates in general to protecting wood from wood destroying organisms, and, in particular, to substantially encapsulating a wooden workpiece in a waterproof thermoplastic sheath together with an effective amount of a water miscible infection controlling composition and, preferably, sufficient moisture to permit the composition to migrate throughout the workpiece.
2. Description of the Prior Art
It is well known that water soluble borates such as, for example, disodium octaborate tetrahydrate will control wood destroying organisms such as insects and fungi in wood and wood products. U.S. Borax, Inc., for example, sells a disodium octaborate tetrahydrate containing product under the "Tim-bor" mark which is intended to be used for this purpose. Such borates and other water soluble infection controlling compositions had generally been limited in their usefulness because, if treated wood were exposed to rain or substantial amounts of other ambient moisture, these water soluble compositions tended to leach out of the wood, leaving it exposed to infection. Treated wood, for example, could not be left exposed to the elements in use, storage or shipment. Thus, wood could not be treated at a central location, transported to and stored in the open at a construction site.
Attempts to seal treated wood to prevent leaching of water soluble compositions generally required careful preparation of the wood surface including thorough drying of the surface after treatment and before the application of sealing agents such as paint or stain. Such stain or paint sealing agents typically depended for their adhesion upon wetting the surface of the boron treated workpieces. Any localized failures in wetting based adhesion systems resulted in rapid overall failure of the system. Typically, the previous infection controlling reagents formed a crystalline deposit on the surfaces of the treated wooden object. Those deposits interfered with the adhesion of prior sealing agents to the surface. Typically, the treating processes did not maintain the wooden piece moist for a long enough period (typically weeks) to permit the reagent to penetrate all the way through the wood. This left most of the reagent on or near the surface with the inner parts of the wood untreated. The drying process which was previously required before the prior sealing agents could be applied produced checking and splitting which left pathways through the treated areas for the infection (termites and the like) to reach the untreated interior. Also, since the prior proposed sealants wet the surface when applied they tended to mix with and bind the reagent which was at the surface, thus rendering it largely ineffective. Since most of the active reagent was at or near the surface, this largely defeated the purpose of the treatment.
It is well known that the presence of moisture in treated woods promotes the migration of the water soluble treating agents into or throughout the wood. See, for example, Knudson et al. U.S. Pat. No. 4,879,083, and Dicker U.S. Pat. No. 4,620,990. The previous perceived need to dry the surface of treated wood prior to sealing it was counterproductive because it tended to remove the moisture which was needed to promote the migration of the treating agents into or throughout the wood, both initially and over the life of the product. Also green wood, that is, wood which had a moisture content of about 20 percent or more, tended to be difficult to seal as previously proposed unless first dried. When dried to the degree previously believed necessary prior to sealing it, the wood was subject to warpage, splitting, and the like. Also the drying process was generally costly.
The results from prior efforts to seal treated wood were generally partially or ineffectively treated wooden workpieces. Such partial or ineffectual treatment left the wood at least partially exposed to infection by wood destroying organisms. Partially sealed and reinforced wooden workpieces such as those proposed by Boyles U.S. Pat. No. 5,326,410 were generally at risk of becoming ineffective due to excessive leaching of the borate and of being weakened by reason of the borate containing bores formed in them.
Previous proposals to use glycols and glycol soluble borates with previously dried lumber were generally unsatisfactory, inter alia, because of economic and environmental factors. See, for example, Palmere et al. U.S. Pat. No. 5,104,664.
Wooden workpieces had previously been sealed in water impervious plastic sheaths to protect them from the elements. See, for example, Totten U.S. Pat. No. 4,181,764. In general the presence of significant amounts of moisture within the sealed sheath had been considered to be undesirable because of the risk of fungus attacking the encapsulated wood.
These and other difficulties of the prior art have been overcome according to the present invention.